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Question

An infinite row of boxes is arranged. Each box has half the volume of the previous box. If the largest box has a volume of $20\text{ cc}$, what is the total volume of all the boxes'?

The correct answer is
$40\text{ cc}$

Infinite Series Volume Calculation

This problem involves finding the sum of an infinite geometric series. The volumes of the boxes form a sequence where each term is half of the previous one.

Identifying Series Parameters

  • The first term (largest box volume), a = $20\text{ cc}$.
  • The common ratio, r, is the factor by which each volume decreases. Since each box has half the volume of the previous one, r = $1/2$.

Sum of Infinite Geometric Series

The formula for the sum (S) of an infinite geometric series is:

$ S = \frac{a}{1-r} $

This formula is valid only if the absolute value of the common ratio is less than 1 (i.e., $|r| < 1$). In this case, $|1/2| < 1$, so the formula can be applied.

Calculating Total Volume

Substitute the values of a and r into the formula:

$ S = \frac{20}{1 - \frac{1}{2}} $

First, calculate the denominator:

$ 1 - \frac{1}{2} = \frac{1}{2} $

Now, perform the division:

$ S = \frac{20}{\frac{1}{2}} = 20 \times 2 = 40 $

The total volume of all the boxes is $40\text{ cc}$.

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Important Questions from Progression (Notes)

  1. The sum of 16 terms of the series $\sqrt{2} + \sqrt{8} + \sqrt{18} + \sqrt{32} + .....$ is :
  2. A pilgrim starts walking for a journey of 115 km. On the first day he covers 7 km, the next day 9 km, and likewise keeps adding 2 km everyday till he reaches 15 km per day which he maintains for the rest of the journey. How many days in all will he take to complete the journey?
  3. If a, b and c are in Geometric Progression and $a^\frac{1}{x} = b^\frac{1}{y} = c^\frac{1}{z}$ then, x, y, z are in ________.

  4. Which of the following statement is true about the geometric series

     $ 1 + r +r^2 + r^3 + ...............; (r > 0) $?

  5. $6240$ रुपये की राशि $30$ किस्तों में इस प्रकार चुकाई जाती है कि प्रत्येक किस्त पिछली किस्त से $10$ रुपये अधिक है । पहली किस्त की मूल्य ____________है।

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